FETs and methods of forming FETs

ABSTRACT

An embodiment is a structure. The structure comprises a fin on a substrate, isolation regions on the substrate, a dielectric region, and a gate structure. The fin includes a first epitaxial portion. The isolation regions are on opposing sides of the fin, and at least the first epitaxial portion of the fin protrudes from between the isolation regions. The dielectric region directly underlies the first epitaxial portion. A material of the dielectric region is different from a material of the isolation regions. The gate structure is along sidewalls and is over an upper surface of the fin. The gate structure defines a channel region in the first epitaxial portion.

BACKGROUND

Semiconductor devices are used in a large number of electronic devices,such as computers, cell phones, and others. Semiconductor devicescomprise integrated circuits that are formed on semiconductor wafers bydepositing many types of thin films of material over the semiconductorwafers, and patterning the thin films of material to form the integratedcircuits. Integrated circuits typically include field-effect transistors(FETs).

Conventionally, planar FETs have been used in integrated circuits.However, with the ever increasing density and decreasing footprintrequirements of modern semiconductor processing, planar FETs maygenerally incur problems when reduced in size. Some of these problemsinclude sub-threshold swing degradation, significant drain inducedbarrier lowering (DIBL), fluctuation of device characteristics, andleakage. Fin field-effect transistors (finFETs) have been studied toovercome some of these problems.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 is an example of a Fin Field-Effect Transistor (finFET) in athree-dimensional view.

FIGS. 2 through 15, 16A-C, 17A-C, 18A-C, 19A-C, 20A-C, 21A-C, 22A-C, and23A-C are cross-sectional views of intermediate stages in themanufacturing of finFETs in accordance with some embodiments.

FIGS. 24A and 24B are a process flow of a process in accordance withsome embodiments.

FIGS. 25 and 26A-C are cross-sectional views of intermediate stagescomprising a modification in the manufacturing of finFETs in accordancewith some embodiments.

FIGS. 27 through 35 and 36A-C are cross-sectional views of intermediatestages in the manufacturing of finFETs in accordance with otherembodiments.

FIGS. 37A and 37B are a process flow of a process in accordance withsome embodiments.

FIGS. 38 and 39A-C are cross-sectional views of intermediate stagescomprising a modification in the manufacturing of finFETs in accordancewith some embodiments.

FIGS. 40 through 42 are cross-sectional views of aspects that can beincorporated into processes and structures in accordance with someembodiments.

FIGS. 43 through 45 are cross-sectional views of aspects that can beincorporated into processes and structures in accordance with someembodiments.

FIGS. 46 through 55 are cross-sectional views of intermediate stages inthe manufacturing of finFETs in accordance with some embodiments.

FIGS. 56A and 56B are a process flow of the process shown in accordancewith some embodiments.

FIG. 57 is a cross-sectional view of an intermediate stage comprising amodification in the manufacturing of finFETs in accordance with someembodiments.

FIGS. 58 through 60 are cross-sectional views of aspects that can beincorporated into processes and structures in accordance with someembodiments.

FIGS. 61 through 63 are transmission electron microscopy (TEM) images ofsamples in accordance with embodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

Fin Field-Effect Transistors (finFETs) and methods of forming the sameare provided in accordance with various embodiments. Intermediate stagesof forming finFETs are illustrated. Some embodiments discussed hereinare discussed in the context of finFETs formed using a gate-lastprocess. In other embodiments, a gate-first process may be used. Also,some embodiments contemplate aspects used in planar devices, such asplanar FETs. Some variations of the embodiments are discussed. One ofordinary skill in the art will readily understand other modificationsthat may be made that are contemplated within the scope of otherembodiments. Although method embodiments are discussed in a particularorder, various other method embodiments may be performed in any logicalorder and may include fewer or more steps described herein.

FIG. 1 illustrates an example of a finFET 30 in a three-dimensionalview. The finFET 30 comprises a fin 36 on a substrate 32. The substrate32 includes isolation regions 34, and the fin 36 protrudes above andfrom between neighboring isolation regions 34. A gate dielectric 38 isalong sidewalls and over a top surface of the fin 36, and a gateelectrode 40 is over the gate dielectric 38. Source/drain regions 42 and44 are disposed in opposite sides of the fin 36 with respect to the gatedielectric 38 and gate electrode 40. FIG. 1 further illustratesreference cross-sections that are used in later figures. Cross-sectionA-A is across a channel, gate dielectric 38, and gate electrode 40 ofthe finFET 30. Cross-section B/C-B/C is perpendicular to cross-sectionA-A and is along a longitudinal axis of the fin 36 and in a directionof, for example, a current flow between the source/drain regions 42 and44. Subsequent figures refer to these reference cross-sections forclarity.

FIGS. 2 through 23C are cross-sectional views of intermediate stages inthe manufacturing of finFETs in accordance with an exemplary embodiment,and FIGS. 24A and 24B are a process flow of the process shown in FIGS. 2through 23C. FIGS. 2 through 15 illustrate reference cross-section A-Aillustrated in FIG. 1, except for multiple finFETs. In FIGS. 16A through23C, figures ending with an “A” designation are illustrated along asimilar cross-section A-A; figures ending with a “B” designation areillustrated along a similar cross-section B/C-B/C and in a first regionon a substrate; and figures ending with a “C” designation areillustrated along a similar cross-section B/C-B/C and in a second regionon a substrate.

FIG. 2 illustrates a substrate 50. Substrate 50 may be a semiconductorsubstrate, such as a bulk semiconductor, a semiconductor-on-insulator(SOI) substrate, or the like, which may be doped (e.g., with a p-type oran n-type dopant) or undoped. The substrate 50 may be a wafer, such as asilicon wafer. Generally, an SOI substrate comprises a layer of asemiconductor material formed on an insulator layer. The insulator layermay be, for example, a buried oxide (BOX) layer, a silicon oxide layer,or the like. The insulator layer is provided on a substrate, typically asilicon or glass substrate. Other substrates, such as a multi-layered orgradient substrate may also be used. In some embodiments, thesemiconductor material of the substrate 50 may include silicon;germanium; a compound semiconductor including silicon carbide, galliumarsenic, gallium phosphide, indium phosphide, indium arsenide, and/orindium antimonide; an alloy semiconductor including SiGe, GaAsP, AlInAs,AlGaAs, GaInAs, GaInP, and/or GaInAsP; or combinations thereof.

The substrate 50 has a first region 50B and a second region 50C. Thefirst region 50B (which corresponds to subsequent figures ending in “B”)can be for forming n-type devices, such as NMOS transistors, such asn-type finFETs. The second region 50C (which corresponds to subsequentfigures ending in “C”) can be for forming p-type devices, such as PMOStransistors, such as p-type finFETs.

FIGS. 3 and 4 illustrate the formation of fins 52 and isolation regions54 between neighboring fins 52. In FIG. 3 and in step 200, fins 52 areformed in the substrate 50. In some embodiments, the fins 52 may beformed in the substrate 50 by etching trenches in the substrate 50. Theetching may be any acceptable etch process, such as a reactive ion etch(RIE), neutral beam etch (NBE), the like, or a combination thereof. Theetch may be anisotropic.

In FIG. 4 and step 202, an insulation material is formed betweenneighboring fins 52 to form the isolation regions 54. The insulationmaterial may be an oxide, such as silicon oxide, a nitride, the like, ora combination thereof, and may be formed by a high density plasmachemical vapor deposition (HDP-CVD), a flowable CVD (FCVD) (e.g., aCVD-based material deposition in a remote plasma system and post curingto make it convert to another material, such as an oxide), the like, ora combination thereof. Other insulation materials formed by anyacceptable process may be used. In the illustrated embodiment, theinsulation material is silicon oxide formed by a FCVD process. An annealprocess may be performed once the insulation material is formed. Furtherin FIG. 4 and in step 204, a planarization process, such as a chemicalmechanical polish (CMP), may remove any excess insulation material andform top surfaces of the isolation regions 54 and top surfaces of thefins 52 that are co-planar.

In FIG. 5 and step 206, a mask 58 is formed over the second region 50Cof the substrate 50 while the first region 50B is exposed. The mask 58may be a photoresist patterned by an acceptable photolithography processor the like. Further in FIG. 5 and in step 208, while the mask 58 is onthe second region 50C, recesses 56 are formed in the fins 52 and/or theisolation regions 54 in the first region 50B. The recesses 56 may beformed by etching using any acceptable etch process, such as a RIE, NBE,tetramethyalammonium hydroxide (TMAH), ammonium hydroxide (NH₄OH), a wetetchant capable of etching silicon with good etch selectivity betweensilicon and a material of the isolation regions 54, the like, or acombination thereof. The etch may be anisotropic. Surfaces of the fins52 are exposed as at least portions of the bottom surfaces of therecesses 56. As illustrated, the bottom surfaces of the recesses 56include all of top surfaces of the fins 52 after an etching process. Inthe illustrated embodiment, the top surfaces of the fins 52 are eachplanar. In other embodiments, the top surfaces of the fins 52 may havedifferent configurations, some of which are discussed below.

In FIG. 6 and step 210, epitaxial fins, or active areas, are formed inthe recesses 56 in the first region 50B. In some embodiments, theepitaxial fins are formed by epitaxially growing a material in therecesses 56, such as by metal-organic CVD (MOCVD), molecular beamepitaxy (MBE), liquid phase epitaxy (LPE), vapor phase epitaxy (VPE),selective epitaxial growth (SEG), the like, or a combination thereof. Asillustrated, each of the epitaxial fins in the first region 50Bcomprises a lower epitaxial portion 60 and an upper epitaxial portion62. The lower epitaxial portions 60 are epitaxially grown on the topsurfaces of the fins 52, and the upper epitaxial portions 62 areepitaxially grown on the lower epitaxial portions 60.

A material of the upper epitaxial portions 62 is different from amaterial of the lower epitaxial portions 60. In some embodiments, thedifferent materials of the upper epitaxial portions 62 and the lowerepitaxial portions 60 allow a significant portion of the lower epitaxialportions 60 to be converted to a dielectric material while the upperepitaxial portions 62 are not significantly converted to a dielectricmaterial. In the illustrated embodiment, the lower epitaxial portions 60are silicon germanium, where the concentration of germanium is equal toor greater than 10% (e.g., Si_(1-x)Ge_(x), where x>=0.10), such asgreater than 30%, and the upper epitaxial portions 62 are silicon. Aswill be discussed below, the silicon germanium of the lower epitaxialportions 60 may be converted to silicon germanium oxide by an oxidationprocess, while the silicon of the upper epitaxial portions 62 are notsignificantly converted to an oxide. In other embodiments, the epitaxialfins can comprise other material, such as silicon, silicon carbide,germanium, a III-V compound semiconductor, a II-VI compoundsemiconductor, or the like. For example, the available materials forforming III-V compound semiconductor include, but are not limited to,InAs, AlAs, GaAs, InP, GaN, InGaAs, InAlAs, GaSb, AlSb, AlP, GaP, andthe like.

The lower epitaxial portions 60 may be buffer layers. Further, the lowerepitaxial portions 60 may be stress relaxation buffer layers. Stressrelaxation buffer layers may be substantially relaxed when the materialof the stress relaxation buffer layer is lattice mismatched to thematerial underlying the stress relaxation buffer layer, such as thematerial of the fins 52. The stress relaxation buffer layer may besubstantially relaxed through plastic relaxation by dislocations beinggenerated in the stress buffer layer and/or through elastic relaxation.The stress relaxation buffer layer may further induce a stress in anoverlying material, such as the upper epitaxial portions 62. When arelaxed layer, such as a stress relaxation buffer layer, is latticemismatched with an overlying layer, such as an upper epitaxial portion62, the overlying layer may be stressed through pseudomorphic epitaxialgrowth. For example, assuming the lower epitaxial portion 60 is relaxedSiGe and the upper epitaxial portion 62 is silicon, the upper epitaxialportion 62 may be tensilely strained, which may be advantageous forn-type devices. Other material combinations may achieve a tensile strainin the upper epitaxial portion 62. In other embodiments, the upperepitaxial portion 62 may be compressively strained, which may beadvantageous for p-type devices. Still in other embodiments, even whenmaterials of a lower epitaxial portion 60 and an upper epitaxial portion62 are lattice mismatched, the upper epitaxial portion 62 may bepartially or substantially relaxed by plastic and/or elastic relaxation.

After the epitaxial fins in the first region 50B are formed, the mask 58is removed. For example, if the mask 58 is a photoresist, the mask 58may be removed by an appropriate ashing process, such as using an oxygenplasma. In other embodiments, the mask 58 may be removed using an etch,a CMP process, or the like. Further in FIG. 6 and in step 212, aplanarization process, such as a CMP process, may be used to form thetop surfaces of the epitaxial fins and the isolation regions 54 to beco-planar, for example, when the epitaxial fins are overgrown above thetop surface of the isolation regions 54.

In FIG. 7 and step 214, the isolation regions 54 are recessed. Theisolation regions 54 are recessed such that epitaxial fins in the firstregion 50B and the fins 52 in the second region 50C protrude frombetween neighboring isolation regions 54. As illustrated, the topsurfaces of the isolation regions 54 are below bottom surfaces of thelower epitaxial portions 60 in the first region 50B. In otherembodiments, the top surfaces of the isolation regions 54 may be atdifferent positions. In some embodiments, the recessing of the isolationregions 54 facilitates conversion to a dielectric material, such as byoxidation, of the lower epitaxial portions 60. The depth to which theisolations regions 54 may be recessed may depend on a process used forsuch conversion, such as an oxidation process. If conversion can beachieved without recessing the isolation regions 54, the recessing canbe omitted, for example. The isolation regions 54 may be recessed usingan acceptable etching process, such as one that is selective to thematerial of the isolation regions 54. For example, a chemical oxideremoval using a CERTAS® etch or an Applied Materials SICONI tool ordilute hydrofluoric (dHF) acid may be used.

In FIG. 8 and step 216, the lower epitaxial portions 60 are converted toa dielectric material 64. In some embodiments, the conversion process isan oxidation process. The oxidation process may use a steam furnace. Forexample, the substrate 50 comprising the lower epitaxial portions 60 maybe placed in a furnace such that the substrate 50 is exposed to a steamenvironment. The steam environment may be generated at a temperaturebetween about 400° C. and about 600° C., such as about 500° C. Water(H₂O) steam may be provided flowing at a flow rate of between about 100sccm and about 1000 sccm. The substrate 50 may be exposed to the steamenvironment in the furnace for a duration between about 0.5 hour andabout 3 hour, such as about 1 hour. As illustrated in FIG. 8, when asteam environment is used for oxidation, the steam may reach the lowerepitaxial portions 60 to convert the lower epitaxial portions 60 to adielectric material 64. Other conversion processes may be used.

In some embodiments where the fins 52 are silicon, the lower epitaxialportions 60 are Si_(1-x)Ge_(x), where x>=0.10, and the upper epitaxialportions 62 are silicon, as discussed above, and an oxidation process isused for the conversion, the lower epitaxial portions 60 may oxidize toform SiGeO faster than the fins 52 and the upper epitaxial portions 62are oxidized, since germanium oxidizes at a greater rate than silicon.Hence, a significant portion of each lower epitaxial portion 60 may beoxidized while very little of the fins 52 and upper epitaxial portions62 are oxidized.

In the illustrated embodiment in FIG. 8, the lower epitaxial portions 60are converted to a dielectric material 64 to an extent such that acontinuous region of the lower epitaxial portion 60 remains between theupper epitaxial portions 62 and respective fins 52. As will be discussedsubsequently, the lower epitaxial portions 60 may be converted to adielectric material 64 to an extent such that a discontinuous region ofthe lower epitaxial portion 60 remains.

In FIG. 9 and step 218, an insulation material 66 is formed betweenneighboring epitaxial fins in the first region 50B and neighboring fins52 in the second region 50C over the isolation regions 54. Theinsulation material 66 may be deposited when the isolation regions 54were previously recessed, such as discussed with respect to FIG. 7. Ifthe isolation regions 54 were not recessed, the insulation material 66may be omitted, for example. The insulation material may be an oxide,such as silicon oxide, a nitride, the like, or a combination thereof,and may be formed by a HDP-CVD, a FCVD, the like, or a combinationthereof. Other insulation materials formed by any acceptable process maybe used. In the illustrated embodiment, the insulation material issilicon oxide formed by a FCVD process. An anneal process may beperformed once the insulation material is formed. Further in FIG. 9 andin step 220, a planarization process, such as a CMP, may remove anyexcess insulation material and form top surfaces of the insulatingmaterial 66 and top surfaces of the epitaxial fins and fins 52 that areco-planar.

In FIG. 10 and step 222, a mask 68 is formed over the first region 50Bof the substrate 50 while the second region 50C is exposed. The mask 68may be a photoresist patterned by an acceptable photolithography processor the like. Further in FIG. 10 and in step 224, while the mask 68 is onthe first region 50B, recesses 69 are formed in the fins 52 and/or theisolation regions 54 in the second region 50C. The recesses 69 may beformed by etching using any acceptable etch process, such as a RIE, NBE,TMAH, ammonium hydroxide, a wet etchant capable of etching silicon withgood etch selectivity between silicon and a material of the isolationregions 54 and insulating material 66, the like, or a combinationthereof. The etch may be anisotropic. Surfaces of the fins 52 areexposed as at least portions of the bottom surfaces of the recesses 69.As illustrated, the bottom surfaces of the recesses 69 include all oftop surfaces of the fins 52 after an etching process. In the illustratedembodiment, the top surfaces of the fins 52 are each planar. In otherembodiments, the top surfaces of the fins 52 may have differentconfigurations, some of which are discussed below. The depth of therecesses 69 may depend on the structure subsequently formed in therecesses 69, as discussed in more detail below.

In FIG. 11 and step 226, epitaxial fins are formed in the recesses 69 inthe second region 50C. In some embodiments, the epitaxial fins areformed by epitaxially growing a material in the recesses 69, such as byMOCVD, MBE, LPE, VPE, SEG, the like, or a combination thereof. Asillustrated, each of the epitaxial fins in the second region 50Ccomprises a lower epitaxial portion 70 and an upper epitaxial portion72. The lower epitaxial portions 70 are epitaxially grown on the topsurfaces of the fins 52, and the upper epitaxial portions 72 areepitaxially grown on the lower epitaxial portions 60. In someembodiments, the lower epitaxial portions 70 may be omitted. In suchembodiments, the depth of the recesses 69 may be lessened, and the upperepitaxial portions 72 may be epitaxially grown on the top surfaces ofthe fins in the second region 50C.

In some embodiments, the epitaxial fins, including the lower epitaxialportions 70 and upper epitaxial portions 72, can comprise as silicon,silicon carbide, silicon germanium, germanium, a III-V compoundsemiconductor, a II-VI compound semiconductor, or the like. For example,the available materials for forming III-V compound semiconductorinclude, but are not limited to, InAs, AlAs, GaAs, InP, GaN, InGaAs,InAlAs, GaSb, AlSb, AlP, GaP, and the like. A material of the upperepitaxial portions 72 may be different from a material of the lowerepitaxial portions 70.

The lower epitaxial portions 70 may be buffer layers. Further, the lowerepitaxial portions 70 may be stress relaxation buffer layers, like thestress buffer layers previously discussed. Similar to that discussedabove, an overlying layer, such as upper epitaxial portions 72, may havestress induced therein from the lattice mismatch with the stress bufferlayer. The upper epitaxial portions 72 may be tensilely or compressivelystrained. Still in other embodiments, even when materials of a lowerepitaxial portion 70 and an upper epitaxial portion 72 are latticemismatched, the upper epitaxial portion 72 may be partially orsubstantially relaxed by plastic and/or elastic relaxation.

After the epitaxial fins in the second region 50C are formed, the mask68 is removed. For example, if the mask 68 is a photoresist, the mask 68may be removed by an appropriate ashing process, such as using an oxygenplasma. In other embodiments, the mask 68 may be removed using an etch,a CMP process, or the like. Further in FIG. 11 and in step 228, aplanarization process, such as a CMP process, may be used to form thetop surfaces of the epitaxial fins in the first region 50B and thesecond region 50C and the insulating material 66 and/or isolationregions 54 to be co-planar, for example, when the epitaxial fins areovergrown above the top surface of the insulating material 66 and/orisolation regions 54.

In FIG. 12 and step 230, the insulating material 66 and/or isolationregions 54 are recessed, such as to form Shallow Trench Isolation (STI)regions. The insulating material 66 and/or isolation regions 54 arerecessed such that epitaxial fins in the first region 50B and in thesecond region 50C protrude from between neighboring insulating material66 and/or isolation regions 54. For simplicity herein, isolation regions54 are illustrated in the figures; however, the isolation regions 54 mayinclude insulating material 66. As illustrated, the top surfaces of theisolation regions 54 are above top surfaces of the lower epitaxialportions 60 and dielectric material 64 in the first region 50B and abovethe lower epitaxial portions 70 in the second region 50C. In otherembodiments, the top surfaces of the isolation regions 54 may be belowtop surfaces and above bottom surfaces of the lower epitaxial portions60 and dielectric material 64 and below top surfaces and above bottomsurfaces of the lower epitaxial portions 70, or the top surfaces of theisolation regions 54 may be below bottom surfaces of the lower epitaxialportions 60 and dielectric material 64 and bottom surfaces of the lowerepitaxial portions 70. Further, the top surfaces of the isolationregions 54 may have a flat surface as illustrated, a convex surface, aconcave surface (such as dishing), or a combination thereof. The topsurfaces of the isolation regions 54 may be formed flat, convex, and/orconcave by an appropriate etch. The isolation regions 54 may be recessedusing an acceptable etching process, such as one that is selective tothe material of the isolation regions 54. For example, a chemical oxideremoval using a CERTAS® etch or an Applied Materials SICONI tool ordilute hydrofluoric (dHF) acid may be used.

In FIGS. 13 and 14 and step 232, appropriate wells may be formed in theepitaxial fins, fins 52, and/or substrate 50. For example, a P well maybe formed in the first region 50B, and an N well may be formed in thesecond region 50C.

As illustrated in FIG. 13, a photoresist 74 is formed over the epitaxialfins and the isolation regions 54 in the first region 50B. Thephotoresist 74 is patterned to expose the second region 50C of thesubstrate 50, such as a PMOS region. The photoresist 74 can be formed byusing a spin-on technique and can be patterned using acceptablephotolithography techniques. Once the photoresist 74 is patterned, ann-type impurity implant 76 is performed in the second region 50C, andthe photoresist 74 may act as a mask to substantially prevent n-typeimpurities from being implanted into the first region 50B, such as anNMOS region. The n-type impurities may be phosphorus, arsenic, or thelike implanted in the first region to a concentration of equal to orless than 10¹⁸ cm⁻³, such as between about 10¹⁷ cm⁻³ and about 10¹⁸cm⁻³. After the implant 76, the photoresist 74 is removed, such as by anacceptable ashing process.

As illustrated in FIG. 14, a photoresist 78 is formed over the epitaxialfins and the isolation regions 54 in the second region 50C. Thephotoresist 78 is patterned to expose the first region 50B of thesubstrate 50, such as the NMOS region. The photoresist 78 can be formedby using a spin-on technique and can be patterned using acceptablephotolithography techniques. Once the photoresist 78 is patterned, ap-type impurity implant 80 may be performed in the first region 50B, andthe photoresist 78 may act as a mask to substantially prevent p-typeimpurities from being implanted into the second region, such as the PMOSregion. The p-type impurities may be boron, BF₂, or the like implantedin the first region to a concentration of equal to or less than 10¹⁸cm⁻³, such as between about 10¹⁷ cm⁻³ and about 10¹⁸ cm⁻³. After theimplant 80, the second photoresist may be removed, such as by anacceptable ashing process.

After the implants 76 and 80, an anneal may be performed to activate thep-type and n-type impurities that were implanted. The implantations mayform a p-well in the first region 50B, e.g., the NMOS region, and ann-well in the second region 50C, e.g., the PMOS region. In someembodiments, the grown materials of the epitaxial fins may be in situdoped during growth, which may obviate the implantations, although insitu and implantation doping may be used together.

A person having ordinary skill in the art will readily understand thatthe process described with respect to FIGS. 2 through 14 is just oneexample of how epitaxial fins may be formed. In other embodiments, adielectric layer can be formed over a top surface of the substrate 50;trenches can be etched through the dielectric layer; the epitaxial finscan be epitaxially grown in the trenches; and the dielectric layer canbe recessed such that the homoepitaxial and/or heteroepitaxialstructures protrude from the dielectric layer to form epitaxial fins. Asdiscussed above, it may be advantageous to epitaxially grow a materialor epitaxial fin structure in the NMOS region different from thematerial or epitaxial fin structure in the PMOS region.

In FIG. 15 and step 234, a dummy dielectric layer 82 is formed on theepitaxial fins. The dummy dielectric layer 82 may be, for example,silicon oxide, silicon nitride, a combination thereof, or the like, andmay be deposited or thermally grown according to acceptable techniques.A dummy gate layer 84 is formed over the dummy dielectric layer 82, anda mask layer 86 is formed over the dummy gate layer 84. The dummy gatelayer 84 may be deposited over the dummy dielectric layer 82 and thenplanarized, such as by a CMP. The mask layer 86 may be deposited overthe dummy gate layer 84. The dummy gate layer 84 may be comprise, forexample, polysilicon, although other materials that have a high etchingselectivity from the etching of isolation regions 54 may also be used.The mask layer 86 may comprise, for example, silicon nitride or thelike. In this example, a single dummy gate layer 84 and a single masklayer 86 are formed across the first region 50B and the second region50C. In other embodiments, separate dummy gate layers may be formed inthe first region 50B and the second region 50C, and separate mask layersmay be formed in the first region 50B and the second region 50C.

In FIGS. 16A, 16B, and 16C and continuing in step 234, the mask layer 86may be patterned using acceptable photolithography and etchingtechniques to form masks 92 in the first region 50B (as illustrated inFIG. 16B) and masks 98 in the second region 50C (as illustrated in FIG.16C). The pattern of the masks 92 and 98 then may be transferred to thedummy gate layer 84 and dummy dielectric layer 82 by an acceptableetching technique to form dummy gates 90 in the first region 50B anddummy gates 96 in the second region 50C. The dummy gates 90 and 96 coverrespective channel regions of the epitaxial fins. The dummy gates 90 and96 may also have a lengthwise direction substantially perpendicular tothe lengthwise direction of respective epitaxial fins.

In FIGS. 17A, 17B, and 17C and step 236, gate seal spacers 100 can beformed on exposed surfaces of respective dummy gates 90 and 96 and/orupper epitaxial portions 62 and 72. A thermal oxidation or a depositionfollowed by an anisotropic etch may form the gate seal spacers 100.

In step 238, implants for lightly doped source/drain (LDD) regions maybe performed. Similar to the implants discussed above in FIGS. 13 and14, a mask, such as a photoresist, may be formed over the first region50B, e.g., NMOS region, while exposing the second region 50C, e.g., PMOSregion, and p-type impurities may be implanted into the exposedepitaxial fins in the second region 50C. The mask may then be removed.Subsequently, a mask, such as a photoresist, may be formed over thesecond region 50C while exposing the first region 50B, and n-typeimpurities may be implanted into the exposed epitaxial fins in the firstregion 50B. The mask may then be removed. The n-type impurities may bethe any of the n-type impurities previously discussed, and the p-typeimpurities may be the any of the p-type impurities previously discussed.The lightly doped source/drain regions may have a concentration ofimpurities of from about 10¹⁵ cm⁻³ to about 10¹⁶ cm⁻³. An anneal may beused to activate the implanted impurities.

Further in FIGS. 17A, 17B, and 17C and in step 240, epitaxialsource/drain regions 102 and 104 are formed in the epitaxial fins. Inthe first region 50B, epitaxial source/drain regions 102 are formed inthe upper epitaxial portions 62 such that each dummy gate 90 is disposedbetween respective neighboring pairs of the epitaxial source/drainregions 102. In some embodiments that epitaxial source/drain regions 102may extend into the lower epitaxial portions 60. In the second region50C, epitaxial source/drain regions 104 are formed in the upperepitaxial portions 72 such that each dummy gate 96 is disposed betweenrespective neighboring pairs of the epitaxial source/drain regions 104.In some embodiments that epitaxial source/drain regions 104 may extendinto the lower epitaxial portions 70.

Epitaxial source/drain regions 102 in the first region 50B, e.g., theNMOS region, may be formed by masking the second region 50C, e.g., thePMOS region, and conformally depositing a dummy spacer layer in thefirst region 50B followed by an anisotropic etch to form dummy gatespacers (not shown) along sidewalls of the dummy gates 90 and/or gateseal spacers 100 in the first region 50B. Then, source/drain regions ofthe epitaxial fins in the first region 50B are etched to form recesses.The epitaxial source/drain regions 102 in the first region 50B areepitaxially grown in the recesses. The epitaxial source/drain regions102 may comprise any acceptable material, such as appropriate for n-typefinFETs. For example, if the upper epitaxial portion 62 is silicon, theepitaxial source/drain regions 102 may comprise silicon, SiC, SiCP, SiP,or the like. The epitaxial source/drain regions 102 may have surfacesraised from respective surfaces of the upper epitaxial portions 62 andmay have facets. Subsequently, the dummy gate spacers in the firstregion 50B are removed, for example, by an etch, as is the mask on thesecond region 50C.

Epitaxial source/drain regions 104 in the second region 50C, e.g., thePMOS region, may be formed by masking the first region 50B, e.g., theNMOS region, and conformally depositing a dummy spacer layer in thesecond region 50C followed by an anisotropic etch to form dummy gatespacers (not shown) along sidewalls of the dummy gates 96 and/or gateseal spacers 100 in the second region 50C. Then, source/drain regions ofthe epitaxial fins in the second region 50C are etched to form recesses.The epitaxial source/drain regions 104 in the second region 50C areepitaxially grown in the recesses. The epitaxial source/drain regions104 may comprise any acceptable material, such as appropriate for p-typefinFETs. For example, if the upper epitaxial portion 72 is silicon, theepitaxial source/drain regions 104 may comprise SiGe, SiGeB, Ge, GeSn,or the like. The epitaxial source/drain regions 104 may have surfacesraised from respective surfaces of the upper epitaxial portions 72 andmay have facets. Subsequently, the dummy gate spacers in the secondregion 50C are removed, for example, by an etch, as is the mask on thefirst region 50B.

In FIGS. 18A, 18B, and 18C and step 242, gate spacers 105 are formed onthe gate seal spacers 100 along sidewalls of the dummy gates 90 and 96.The gate spacers 105 may be formed by conformally depositing a materialand subsequently anisotropically etching the material. The material ofthe gate spacers 105 may be silicon nitride, SiCN, a combinationthereof, or the like.

The epitaxial source/drain regions 102 and 104 and/or epitaxial fins maybe implanted with dopants to form source/drain regions, similar to theprocess previously discussed for forming lightly doped source/drainregions, followed by an anneal. The source/drain regions may have animpurity concentration of between about 10¹⁹ cm⁻³ and about 10²¹ cm⁻³.The n-type impurities for source/drain regions in the first region 50B,e.g., the NMOS region, may be any of the n-type impurities previouslydiscussed, and the p-type impurities for source/drain regions in thesecond region 50C, e.g., the PMOS region, may be any of the p-typeimpurities previously discussed. In other embodiments, the epitaxialsource/drain regions 102 and 104 may be in situ doped during growth.

In FIGS. 19A, 19B, and 19C and step 244, an Inter-Layer Dielectric (ILD)106 is deposited over the structure illustrated in FIGS. 18A, 18B, and18C. ILD 106 is formed of a dielectric material such as Phospho-SilicateGlass (PSG), Boro-Silicate Glass (BSG), Boron-Doped Phospho-SilicateGlass (BPSG), undoped Silicate Glass (USG), or the like, and may bedeposited by any suitable method, such as chemical vapor deposition(CVD), plasma-enhanced CVD (PECVD), or FCVD.

In FIGS. 20A, 20B, and 20C and step 246, a planarization process, suchas a CMP, may be performed to level the top surface of ILD 106 with thetop surfaces of the dummy gates 90 and 96. The CMP may also remove themasks 92 and 98 on the dummy gates 90 and 96. Accordingly, top surfacesof the dummy gates 90 and 96 are exposed through the ILD 106.

In FIGS. 21A, 21B, and 21C and step 248, the dummy gates 90 and 96, gateseal spacers 100, and portions of the dummy dielectric layer 82 directlyunderlying the dummy gates 90 and 96 are removed in an etching step(s),so that recesses 108 are formed. Each recess 108 exposes a channelregion of a respective epitaxial fin. Each channel region is disposedbetween neighboring pairs of epitaxial source/drain regions 102 and 104.During the removal, the dummy dielectric layer 82 may be used as an etchstop layer when the dummy gates 90 and 96 are etched. The dummydielectric layer 82 and gate seal spacers 100 may then be removed afterthe removal of the dummy gates 90 and 96.

In FIGS. 22A, 22B, and 22C and step 250, gate dielectric layers 110 and114 and gate electrodes 112 and 116 are formed for replacement gates.Gate dielectric layers 110 and 114 are deposited conformally in recesses108, such as on the top surfaces and the sidewalls of the epitaxial finsand on sidewalls of the gate spacers 105, and on a top surface of theILD 106. In accordance with some embodiments, gate dielectric layers 110and 114 comprise silicon oxide, silicon nitride, or multilayers thereof.In other embodiments, gate dielectric layers 110 and 114 comprise ahigh-k dielectric material, and in these embodiments, gate dielectriclayers 110 and 114 may have a k value greater than about 7.0, and mayinclude a metal oxide or a silicate of Hf, Al, Zr, La, Mg, Ba, Ti, Pb,and combinations thereof. The formation methods of gate dielectriclayers 110 and 114 may include Molecular-Beam Deposition (MBD), AtomicLayer Deposition (ALD), PECVD, and the like.

Next, gate electrodes 112 and 116 are deposited over gate dielectriclayers 110 and 114, respectively, and fill the remaining portions of therecesses 108. Gate electrodes 112 and 116 may comprise ametal-containing material such as TiN, TaN, TaC, Co, Ru, Al,combinations thereof, or multi-layers thereof. After the filling of gateelectrodes 112 and 116, in step 252, a planarization process, such as aCMP, may be performed to remove the excess portions of gate dielectriclayers 110 and 114 and the material of gate electrodes 112 and 116,which excess portions are over the top surface of ILD 106. The resultingremaining portions of material of gate electrodes 112 and 116 and gatedielectric layers 110 and 114 thus form replacement gates of theresulting finFETs.

The formation of the gate dielectric layers 110 and 114 may occursimultaneously such that the gate dielectric layers 110 and 114 comprisethe same materials, and the formation of the gate electrodes 112 and 116may occur simultaneously such that the gate electrodes 112 and 116comprise the same materials. However, in other embodiments, the gatedielectric layers 110 and 114 may be formed by distinct processes, suchthat the gate dielectric layers 110 and 114 may comprise differentmaterials, and the gate electrodes 112 and 116 may be formed by distinctprocesses, such that the gate electrodes 112 and 116 may comprisedifferent materials. Various masking steps may be used to mask andexpose appropriate regions when using distinct processes.

In FIGS. 23A, 23B, and 23C, an ILD 118 is deposited over ILD 106 in step254, and contacts 120 and 122 are formed through ILD 118 and ILD 106 instep 256. ILD 118 is formed of a dielectric material such as PSG, BSG,BPSG, USG, or the like, and may be deposited by any suitable method,such as CVD and PECVD. Openings for contacts 120 and 122 are formedthrough the ILDs 106 and 118. The openings may be formed usingacceptable photolithography and etching techniques. A liner, such as adiffusion barrier layer, an adhesion layer, or the like, and aconductive material are formed in the openings. The liner may includetitanium, titanium nitride, tantalum, tantalum nitride, or the like. Theconductive material may be copper, a copper alloy, silver, gold,tungsten, aluminum, nickel, or the like. A planarization process, suchas a CMP, may be performed to remove excess material from a surface ofthe ILD 118. The remaining liner and conductive material form contacts120 and 122 in the openings. An anneal process may be performed to forma silicide at the interface between the epitaxial source/drain regions102 and 104 and the contacts 120 and 122, respectively. Contacts 120 arephysically and electrically coupled to the epitaxial source/drainregions 102, and contacts 122 are physically and electrically coupled tothe epitaxial source/drain regions 104.

Although not explicitly shown, a person having ordinary skill in the artwill readily understand that further processing steps may be performedon the structure in FIGS. 23A, 23B, and 23C. For example, variousInter-Metal Dielectrics (IMD) and their corresponding metallizations maybe formed over ILD 118.

FIGS. 25, 26A, 26B, and 26C illustrate a modification to the process andstructures discussed with respect to FIGS. 2 through 24B. FIG. 25illustrates a cross-sectional view of a structure after processingthrough the processes discussed with respect to FIGS. 2 through 7 andafter a conversion process. In FIG. 25, the lower epitaxial portions 60are converted to a dielectric material 64. The conversion process may besimilar to that discussed above with respect to FIG. 8, and may be, forexample, for a longer duration, at a higher temperature, the like, or acombination thereof. In the illustrated embodiment in FIG. 25, the lowerepitaxial portions 60 are converted to a dielectric material 64 to anextent such that a discontinuous region of the lower epitaxial portion60 remains between the upper epitaxial portions 62 and respective fins52. Discontinuities 130 are illustrated. Processing may then proceed asdiscussed with respect to FIGS. 9 through 23C to achieve the structureillustrated in FIGS. 26A, 26B, and 26C. The structure illustrated inFIGS. 26A, 26B, and 26C is the same as the structure in FIGS. 23A, 23B,and 23C, except with the discontinuous regions of the lower epitaxialportions 60.

FIGS. 27 through 36C are cross-sectional views of intermediate stages inthe manufacturing of finFETs in accordance with another exemplaryembodiment, and FIGS. 37A and 37B are a process flow of the processshown in FIGS. 27 through 36C. FIGS. 27 through 35 illustrate referencecross-section A-A illustrated in FIG. 1, except for multiple finFETs. InFIGS. 36A, 36B, and 36C, figures ending with an “A” designation areillustrated along a similar cross-section A-A; figures ending with a “B”designation are illustrated along a similar cross-section B/C-B/C and ina first region on a substrate; and figures ending with a “C” designationare illustrated along a similar cross-section B/C-B/C and in a secondregion on a substrate.

Processing first proceeds as discussed with respect to FIGS. 2 through 4and steps 200 through 204. In FIG. 27 and step 260, recesses 56 areformed in the fins 52 and/or the isolation regions 54 in the firstregion 50B and the second region 50C, such as simultaneously. Therecesses 56 may be formed by etching using any acceptable etch process.Surfaces of the fins 52 are exposed as at least portions of the bottomsurfaces of the recesses 56. As illustrated, the bottom surfaces of therecesses 56 include all of top surfaces of the fins 52 after an etchingprocess. In the illustrated embodiment, the top surfaces of the fins 52are each planar. In other embodiments, the top surfaces of the fins 52may have different configurations, some of which are discussed below.

In FIG. 28 and step 262, epitaxial fins are formed in the recesses 56 inthe first region 50B and the second region 50C. In some embodiments, theepitaxial fins are formed by epitaxially growing a material in therecesses 56. As illustrated, each of the epitaxial fins in the firstregion 50B and the second region 50C comprises a lower epitaxial portion60 and an upper epitaxial portion 62. The lower epitaxial portions 60are epitaxially grown on the top surfaces of the fins 52, and the upperepitaxial portions 62 are epitaxially grown on the lower epitaxialportions 60.

As previously discussed, a material of the upper epitaxial portions 62is different from a material of the lower epitaxial portions 60. In someembodiments, the different materials of the upper epitaxial portions 62and the lower epitaxial portions 60 allow a significant portion of thelower epitaxial portions 60 to be converted to a dielectric materialwhile the upper epitaxial portions 62 are not significantly converted toa dielectric material. In the illustrated embodiment, the lowerepitaxial portions 60 are silicon germanium, where the concentration ofgermanium is equal to or greater than 10% (e.g., Si_(1-x)Ge_(x), wherex>=0.10), such as greater than 30%, and the upper epitaxial portions 62are silicon. In other embodiments, the epitaxial fins can comprise othermaterial, such as silicon, silicon carbide, germanium, a III-V compoundsemiconductor, a II-VI compound semiconductor, or the like. For example,the available materials for forming III-V compound semiconductorinclude, but are not limited to, InAs, AlAs, GaAs, InP, GaN, InGaAs,InAlAs, GaSb, AlSb, AlP, GaP, and the like.

The lower epitaxial portions 60 may be buffer layers, such as stressrelaxation buffer layers, as discussed above. The stress relaxationbuffer layer may further induce a stress in an overlying material, suchas the upper epitaxial portions 62. The upper epitaxial portion 62 maybe tensilely or compressively strained or may be partially orsubstantially relaxed, as discussed above.

In step 212, a planarization process, such as a CMP process, may be usedto form the top surfaces of the epitaxial fins and the isolation regions54 to be co-planar, for example, when the epitaxial fins are overgrownabove the top surface of the isolation regions 54.

In FIG. 29 and step 214, the isolation regions 54 are recessed. Theisolation regions 54 are recessed such that epitaxial fins in the firstregion 50B and the second region 50C protrude from between neighboringisolation regions 54. As illustrated, the top surfaces of the isolationregions 54 are above top surfaces of the lower epitaxial portions 60. Inother embodiments, the top surfaces of the isolation regions 54 may bebelow top surfaces and above bottom surfaces of the lower epitaxialportions 60, or the top surfaces of the isolation regions 54 may bebelow bottom surfaces of the lower epitaxial portions 60. In someembodiments, the recessing of the isolation regions 54 facilitatesconversion to a dielectric material, such as by oxidation, of the lowerepitaxial portions 60. The depth to which the isolations regions 54 maybe recessed may depend on a process used for such conversion, such asoxidation. If conversion can be achieved without recessing the isolationregions 54, the recessing can be omitted, for example. The isolationregions 54 may be recessed using an acceptable etching process.

In FIG. 30 and step 216, the lower epitaxial portions 60 are convertedto a dielectric material 64. In some embodiments, the conversion processis an oxidation, such as discussed above. Other conversion processes maybe used.

In some embodiments where the fins 52 are silicon, the lower epitaxialportions 60 are Si_(1-x)Ge_(x), where x>=0.10, and the upper epitaxialportions 62 are silicon, as discussed above, and an oxidation process isused for the conversion, the lower epitaxial portions 60 may oxidize toform SiGeO faster than the fins 52 and the upper epitaxial portions 62are oxidized, since SiGe oxidizes at a greater rate than silicon. Hence,a significant portion of each lower epitaxial portion 60 may be oxidizedwhile very little of the fins 52 and upper epitaxial portions 62 areoxidized.

In the illustrated embodiment in FIG. 30, the lower epitaxial portions60 are converted to a dielectric material 64 to an extent such that acontinuous region of the lower epitaxial portion 60 remains between theupper epitaxial portions 62 and respective fins 52. As will be discussedsubsequently, the lower epitaxial portions 60 may be converted to adielectric material 64 to an extent such that a discontinuous region ofthe lower epitaxial portion 60 remains.

In FIG. 31 and step 218, an insulation material 66 is formed betweenneighboring epitaxial fins in the first region 50B and the second region50C over the isolation regions 54. The insulation material 66 may bedeposited when the isolation regions 54 were previously recessed, suchas discussed with respect to FIG. 29. If the isolation regions 54 werenot recessed, the insulation material 66 may be omitted, for example.Further in FIG. 31 and in step 220, a planarization process, such as aCMP, may remove any excess insulation material and form top surfaces ofthe insulating material 66 and top surfaces of the epitaxial fins thatare co-planar.

In FIG. 32 and step 222, a mask 68 is formed over the first region 50Bof the substrate 50 while the second region 50C is exposed. The mask 68may be a photoresist patterned by an acceptable photolithographyprocess, or the like. Further in FIG. 32 and in step 264, while the mask68 is on the first region 50B, recesses 140 are formed in the upperepitaxial portions 62 and/or the isolation regions 54 in the secondregion 50C. The recesses 140 may be formed by etching using anyacceptable etch process, such as a RIE, NBE, TMAH, ammonium hydroxide, awet etchant capable of etching silicon with good etch selectivitybetween silicon and a material of the isolation regions 54 andinsulating material 66, the like, or a combination thereof. The etch maybe anisotropic.

As illustrated, at least a portion of the upper epitaxial portions 62 inthe second region 50C remain as template layers 142. Surfaces of thetemplate layers 142 are exposed as at least portions of the bottomsurfaces of the recesses 140. As illustrated, the bottom surfaces of therecesses 140 include all of top surfaces of the template layers 142after an etching process. In the illustrated embodiment, the topsurfaces of the template layers 142 are each planar. In otherembodiments, the top surfaces of the template layers 142 may havedifferent configurations, some of which are discussed below. Asdiscussed below, the template layers 142 may be used as a template toepitaxially grow a material.

In FIG. 34 and step 266, epitaxial fins are formed in the recesses 140in the second region 50C. In some embodiments, the epitaxial fins areformed by epitaxially growing a material in the recesses 140, such as byMOCVD, MBE, LPE, VPE, SEG, the like, or a combination thereof. Asillustrated, each of the epitaxial fins in the second region 50Ccomprises an upper epitaxial portion 144. The upper epitaxial portions144 are epitaxially grown on the template layers 142.

In some embodiments, the epitaxial fins, including the upper epitaxialportions 144, can comprise as silicon, silicon carbide, silicongermanium, germanium, a III-V compound semiconductor, a II-VI compoundsemiconductor, or the like. For example, the available materials forforming III-V compound semiconductor include, but are not limited to,InAs, AlAs, GaAs, InP, GaN, InGaAs, InAlAs, GaSb, AlSb, AlP, GaP, andthe like. A material of the upper epitaxial portions 144 may bedifferent from a material of the template layers 142.

After the epitaxial fins in the second region 50C are formed, the mask68 is removed. For example, if the mask 68 is a photoresist, the mask 68may be removed by an appropriate ashing process, such as using an oxygenplasma. In other embodiments, the mask 68 may be removed using an etch,a CMP process, or the like. Further in FIG. 34 and in step 228, aplanarization process, such as a CMP process, may be used to form thetop surfaces of the epitaxial fins in the first region 50B and thesecond region 50C and the insulating material 66 and/or isolationregions 54 to be co-planar, for example, when the epitaxial fins areovergrown above the top surface of the insulating material 66 and/orisolation regions 54.

In FIG. 35 and step 230, the insulating material 66 and/or isolationregions 54 are recessed, such as to form STI regions. The insulatingmaterial 66 and/or isolation regions 54 are recessed such that epitaxialfins in the first region 50B and in the second region 50C protrude frombetween neighboring insulating material 66 and/or isolation regions 54.For simplicity herein, isolation regions 54 are illustrated in thefigures; however, the isolation regions 54 may include insulatingmaterial 66. As illustrated, the top surfaces of the isolation regions54 are above top surfaces of the lower epitaxial portions 60 anddielectric material 64 in the first region 50B and the second region50C. In other embodiments, the top surfaces of the isolation regions 54may be below top surfaces and above bottom surfaces of the lowerepitaxial portions 60 and dielectric material 64, or the top surfaces ofthe isolation regions 54 may be below bottom surfaces of the lowerepitaxial portions 60 and dielectric material 64. Further, the topsurfaces of the isolation regions 54 may have a flat surface asillustrated, a convex surface, a concave surface (such as dishing), or acombination thereof. The top surfaces of the isolation regions 54 may beformed flat, convex, and/or concave by an appropriate etch. Theisolation regions 54 may be recessed using an acceptable etchingprocess.

Processing may then proceed as discussed with respect to FIGS. 13through 23C and steps 232 through 256 to achieve the structureillustrated in FIGS. 36A, 36B, and 36C. The structure illustrated inFIGS. 36A, 36B, and 36C is the same as the structure in FIGS. 23A, 23B,and 23C, except with the lower epitaxial portions 60, dielectricmaterial 64, template layers 142, and upper epitaxial portions 144 inthe second region 50C.

FIGS. 38, 39A, 39B, and 39C illustrate a modification to the process andstructures discussed with respect to FIGS. 2 through 4, 27 through 35,and 13 through 23C. FIG. 38 illustrates a cross-sectional view of astructure after processing through the processes discussed with respectto FIGS. 2 through 4 and 27 through 29 and after a conversion process.In FIG. 38, the lower epitaxial portions 60 are converted to adielectric material 64. The conversion process may be similar to thatdiscussed above with respect to FIG. 30, and may be, for example, for alonger duration, at a higher temperature, the like, or a combinationthereof. In the illustrated embodiment in FIG. 38, the lower epitaxialportions 60 are converted to a dielectric material 64 to an extent suchthat a discontinuous region of the lower epitaxial portion 60 remainsbetween the upper epitaxial portions 62 and respective fins 52.Discontinuities 130 are illustrated. Processing may then proceed asdiscussed with respect to FIGS. 31 through 35 and 13 through 23C toachieve the structure illustrated in FIGS. 39A, 39B, and 39C. Thestructure illustrated in FIGS. 39A, 39B, and 39C is the same as thestructure in FIGS. 36A, 36B, and 36C, except with the discontinuousregions of the lower epitaxial portions 60.

FIGS. 40 through 42 illustrate features that can be incorporated intoembodiments. In FIG. 40, top surfaces of the fins 52 have aconfiguration, such as being convex (as illustrated), flat, or concave.These top surfaces may be formed by the recessing in FIG. 5, 10, or 27.The top surface configuration of the fins 52 can be formed by using anappropriate etching process, like a wet etch such as hot ammonia to forma concave or convex surface or a dry plasma etch to form a flat surface.Also in FIG. 40, top surfaces of the lower epitaxial portions 60 have aconfiguration, such as being concave (as illustrated), flat, or convex.These top surfaces may be formed by over growing the lower epitaxialportions and performing an etch-back process in FIG. 6, 11, or 28. Thetop surface configuration of the lower epitaxial portions 60 can beformed by using an appropriate etching process, like a wet etch such ashot ammonia to form a concave or convex surface or a dry plasma etch toform a flat surface.

FIG. 41 illustrates a structure after converting the lower epitaxialportions 60 to a dielectric material 64 where continuous portions of thelower epitaxial portions 60 remain, like in FIGS. 8 and 30. FIG. 42illustrates a structure after converting the lower epitaxial portions 60to a dielectric material 64 where discontinuous portions of the lowerepitaxial portions 60 remain with discontinuities 130, like in FIGS. 25and 38. As indicated, the features illustrated in FIG. 40 through 42 forthe first region 50B may or may not be present simultaneously with thefeatures illustrated for the second region 50C depending on howprocessing is performed. These features are illustrated in thesediscrete drawings for ease of illustration, and a person of ordinaryskill in the art will readily understand how these features can beincorporated into the processes based on this discussion.

FIGS. 43 through 45 illustrate features that can be incorporated intoembodiments. In FIG. 43, top surfaces of the fins 52 have aconfiguration, such as being a V-shape (as illustrated), which couldfurther be symmetrical or asymmetrical. These top surfaces may be formedby the recessing in FIG. 5, 10, or 27. The top surface configuration ofthe fins 52 can be formed by using an appropriate etching processselective to a crystallographic plane, such as a (111) plane. Also inFIG. 43, top surfaces of the template layers 142 have a configuration,such as being a V-shape (as illustrated), which could further besymmetrical or asymmetrical. These top surfaces may be formed by therecessing in FIG. 33. The top surface configuration of the templatelayers 142 can be formed by using an appropriate etching processselective to a crystallographic plane, such as a (111) plane.

FIG. 44 illustrates a structure after converting the lower epitaxialportions 60 to a dielectric material 64 where continuous portions of thelower epitaxial portions 60 remain, like in FIGS. 8 and 30. FIG. 45illustrates a structure after converting the lower epitaxial portions 60to a dielectric material 64 where discontinuous portions of the lowerepitaxial portions 60 remain with discontinuities 130, like in FIGS. 25and 38. As indicated, the features illustrated in FIG. 43 through 45 forthe first region 50B may or may not be present simultaneously with thefeatures illustrated for the second region 50C depending on howprocessing is performed. These features are illustrated in thesediscrete drawings for ease of illustration, and a person of ordinaryskill in the art will readily understand how these features can beincorporated into the processes based on this discussion.

FIGS. 46 through 55 are cross-sectional views of intermediate stages inthe manufacturing of finFETs in accordance with an exemplary embodiment,and FIGS. 56A and 56B are a process flow of the process shown in FIGS.46 through 55. FIGS. 46 through 555 illustrate reference cross-sectionA-A illustrated in FIG. 1, except for multiple finFETs.

FIG. 46 illustrates a substrate 50 like the substrate 50 in FIG. 2. Thesubstrate 50 has a first region 50B and a second region 50C. Asdiscussed with respect to FIG. 2, the first region 50B can be forforming n-type devices, such as NMOS transistors, such as n-typefinFETs. As discussed with respect to FIG. 2, the second region 50C canbe for forming p-type devices, such as PMOS transistors, such as p-typefinFETs.

In FIG. 47 and step 300, a lower epitaxial layer 150 (e.g., a blanketlayer) and an upper epitaxial layer 152 (e.g., a blanket layer) areformed in both the first region 50B and the second region 50C of thesubstrate 50. The lower epitaxial layer 150 is formed on the substrate50, and the upper epitaxial layer 152 is formed on the lower epitaxiallayer 150. In some embodiments, the lower epitaxial layer 150 and theupper epitaxial layer 152 are formed by epitaxially growing a material,such as by MOCVD, MBE, LPE, VPE, SEG, the like, or a combinationthereof. Example materials of the lower epitaxial layer 150 and theupper epitaxial layer 152 are discussed subsequently after additionalcontext is discussed.

In FIG. 48 and step 302, a mask 154 is formed over the second region 50Cof the substrate 50 while the first region 50B is exposed. The mask 154may be a photoresist patterned by an acceptable photolithography processor the like. While the mask 154 is over the second region 50C, an etch,as shown in step 304, is performed to remove the upper epitaxial layer152 and the lower epitaxial layer 150 in the first region 50B. Theetching may be any acceptable etch process, such as a RIE, NBE, thelike, or a combination thereof. Subsequently, in step 306, a lowerepitaxial layer 156 (e.g., a blanket layer) and an upper epitaxial layer158 (e.g., a blanket layer) are formed in the first region 50B of thesubstrate 50. The lower epitaxial layer 156 is formed on the substrate50, and the upper epitaxial layer 158 is formed on the lower epitaxiallayer 156. In some embodiments, the lower epitaxial layer 156 and theupper epitaxial layer 158 are formed by epitaxially growing a material,such as by MOCVD, MBE, LPE, VPE, SEG, the like, or a combinationthereof. Example materials of the lower epitaxial layer 156 and theupper epitaxial layer 158 are discussed subsequently after additionalcontext is discussed. In step 308, a planarization process, such as aCMP, may remove any remaining mask 154 and form top surfaces of theupper epitaxial layers 152 and 158 that are co-planar.

In some embodiments, the lower epitaxial layer 150 may not be removedfrom the first region 50B, and may replace the lower epitaxial layer 156in the first region 50B. Further, each epitaxial layer may comprise oneor more distinct layers that may be desirable for a given application.

In FIGS. 49 and 50 and step 310 (similar to step 232 and the processsteps in FIGS. 13 and 14), appropriate wells may be formed in the upperepitaxial layers 158 and 152, lower epitaxial layers 156 and 150, and/orsubstrate 50. For example, a P well may be formed in the first region50B, and an N well may be formed in the second region 50C.

As illustrated in FIG. 49, a photoresist 160 is formed over the upperepitaxial layer 158 in the first region 50B. The photoresist 160 ispatterned to expose the second region 50C of the substrate 50, such as aPMOS region. The photoresist 160 can be formed by using a spin-ontechnique and can be patterned using acceptable photolithographytechniques. Once the photoresist 160 is patterned, an n-type impurityimplant 162 is performed in the second region 50C, and the photoresist160 may act as a mask to substantially prevent n-type impurities frombeing implanted into the first region 50B, such as an NMOS region. Then-type impurities may be phosphorus, arsenic, or the like implanted inthe first region to a concentration of equal to or less than 10¹⁸ cm⁻³,such as between about 10¹⁷ cm⁻³ and about 10¹⁸ cm⁻³. After the implant162, the photoresist 160 is removed, such as by an acceptable ashingprocess.

As illustrated in FIG. 50, a photoresist 164 is formed over the upperepitaxial layer 152 in the second region 50C. The photoresist 164 ispatterned to expose the first region 50B of the substrate 50, such asthe NMOS region. The photoresist 164 can be formed by using a spin-ontechnique and can be patterned using acceptable photolithographytechniques. Once the photoresist 164 is patterned, a p-type impurityimplant 166 may be performed in the first region 50B, and thephotoresist 164 may act as a mask to substantially prevent p-typeimpurities from being implanted into the second region, such as the PMOSregion. The p-type impurities may be boron, BF₂, or the like implantedin the first region to a concentration of equal to or less than 10¹⁸cm⁻³, such as between about 10¹⁷ cm⁻³ and about 10¹⁸ cm⁻³. After theimplant 166, the second photoresist may be removed, such as by anacceptable ashing process.

After the implants 162 and 166, an anneal may be performed to activatethe p-type and n-type impurities that were implanted. The implantationsmay form a p-well in the first region 50B, e.g., the NMOS region, and ann-well in the second region 50C, e.g., the PMOS region. In someembodiments, the grown materials of the epitaxial layers may be in situdoped during growth, which may obviate the implantations, although insitu and implantation doping may be used together.

In FIG. 51 and step 312 (similar to step 200 and the process steps inFIG. 3), fins 52 and epitaxial fins are formed. The epitaxial fins inthe first region 50B comprise lower epitaxial portions 60 and upperepitaxial portions 62 formed from the lower epitaxial layer 156 andupper epitaxial layer 158, respectively. The epitaxial fins in thesecond region 50C comprise lower epitaxial portions 70 and upperepitaxial portions 72 formed from the lower epitaxial layer 150 andupper epitaxial layer 152, respectively. In some embodiments, the fins52 and epitaxial fins may be formed by etching trenches in the upperepitaxial layers 152 and 158, lower epitaxial layers 150 and 156, andsubstrate 50. The etching may be any acceptable etch process, such as areactive ion etch (RIE), neutral beam etch (NBE), the like, or acombination thereof. The etch may be anisotropic.

Similar to previous discussion, a material of the upper epitaxial layer158 (and hence, the upper epitaxial portions 62) is different from amaterial of the lower epitaxial layer 156 (and hence, the lowerepitaxial portions 60). In some embodiments, the different materials ofthe upper epitaxial portions 62 and the lower epitaxial portions 60allow a significant portion of the lower epitaxial portions 60 to beconverted to a dielectric material while the upper epitaxial portions 62are not significantly converted to a dielectric material. In theillustrated embodiment, the lower epitaxial portions 60 are silicongermanium, where the concentration of germanium is equal to or greaterthan 10% (e.g., Si_(1-x)Ge_(x), where x>=0.10), such as greater than30%, and the upper epitaxial portions 62 are silicon. In otherembodiments, the epitaxial fins can comprise other material, such assilicon, silicon carbide, germanium, a III-V compound semiconductor, aII-VI compound semiconductor, or the like. For example, the availablematerials for forming III-V compound semiconductor include, but are notlimited to, InAs, AlAs, GaAs, InP, GaN, InGaAs, InAlAs, GaSb, AlSb, AlP,GaP, and the like.

The lower epitaxial portions 60 may be buffer layers, such as stressrelaxation buffer layers, as discussed above. The stress relaxationbuffer layer may further induce a stress in an overlying material, suchas the upper epitaxial portions 62. The upper epitaxial portion 62 maybe tensilely or compressively strained or may be partially orsubstantially relaxed, as discussed above.

Similar to previous discussion, in some embodiments, the upper epitaxiallayer 152 (and hence, the upper epitaxial portions 72) and the lowerepitaxial layer 150 (and hence, the lower epitaxial portions 70) cancomprise as silicon, silicon carbide, silicon germanium, germanium, aIII-V compound semiconductor, a II-VI compound semiconductor, or thelike. For example, the available materials for forming III-V compoundsemiconductor include, but are not limited to, InAs, AlAs, GaAs, InP,GaN, InGaAs, InAlAs, GaSb, AlSb, AlP, GaP, and the like. A material ofthe upper epitaxial portions 72 may be different from a material of thelower epitaxial portions 70.

The lower epitaxial portions 70 may be buffer layers. Further, the lowerepitaxial portions 70 may be stress relaxation buffer layers, like thestress buffer layers previously discussed. Similar to that discussedabove, an overlying layer, such as upper epitaxial portions 72, may havestress induced therein from the lattice mismatch with the stress bufferlayer. The upper epitaxial portions 72 may be tensilely or compressivelystrained. Still in other embodiments, even when materials of a lowerepitaxial portion 70 and an upper epitaxial portion 72 are latticemismatched, the upper epitaxial portion 72 may be partially orsubstantially relaxed by plastic and/or elastic relaxation.

In FIG. 52 and step 314, a mask 168 is formed over the fins 52 andepitaxial fins in the second region 50C of the substrate 50 while thefirst region 50B is exposed. The mask 168 may comprise silicon nitride(SiN), silicon carbon nitride (SiCN), silicon oxide (SiO), siliconoxynitride (SiO_(x)N_(y)), a combination thereof, or the like, depositedby CVD, PECVD, ALD, LPCVD, or the like. The deposition of the mask 168may be conformal over the first region 50B and the second region 50C. Amask, such as a photoresist, can be formed over the second region 50C ofthe substrate 50 while the first region 50B is exposed, such as by anacceptable photolithography process or the like. Then, an acceptableetching process, such as a wet or dry etch, can be performed to removethe mask 168 from the first region 50B. In other embodiments, the mask168 may be omitted, for example, when the lower epitaxial portions 70are to be converted to a dielectric material during subsequent steps.

In FIG. 53 and step 216 as discussed with respect to FIG. 8, the lowerepitaxial portions 60 are converted to a dielectric material 64. In someembodiments, the conversion process is an oxidation, such as discussedabove. Other conversion processes may be used. In the illustratedembodiment in FIG. 53, the lower epitaxial portions 60 are converted toa dielectric material 64 to an extent such that a continuous region ofthe lower epitaxial portion 60 remains between the upper epitaxialportions 62 and respective fins 52. As will be discussed subsequently,the lower epitaxial portions 60 may be converted to a dielectricmaterial 64 to an extent such that a discontinuous region of the lowerepitaxial portion 60 remains.

In FIG. 54, the mask 168 is removed in step 312, and isolation regions54 are formed in step 320 (similar to step 202 and processing discussedwith respect to FIG. 4). The mask 168 may be removed by an etchselective to the material of the mask 168, and may be a wet etch.Subsequently, an insulation material is formed between neighboring fins52 and epitaxial fins to form the isolation regions 54. The insulationmaterial may be an oxide, such as silicon oxide, a nitride, the like, ora combination thereof, and may be formed by HDP-CVD, FCVD, the like, ora combination thereof. Other insulation materials formed by anyacceptable process may be used. In the illustrated embodiment, theinsulation material is silicon oxide formed by a FCVD process. An annealprocess may be performed once the insulation material is formed. Furtherin FIG. 54 and in step 322 (similar to step 204), a planarizationprocess, such as a CMP, may remove any excess insulation material andform top surfaces of the isolation regions 54 and top surfaces of theepitaxial fins that are co-planar. It should be noted that differentmaterials may be incorporated as the upper epitaxial portions 62 and/or72 after the planarization process. For example, appropriate masking andetching may be performed to remove upper epitaxial portions 62 and/or72, and a different material may be epitaxially grown in the recessesformed by the removal of upper epitaxial portions 62 and/or 72.

In FIG. 55 and step 324 (similar to step 230 and processing in FIG. 12),the isolation regions 54 are recessed, such as to form STI regions. Theisolation regions 54 are recessed such that epitaxial fins in the firstregion 50B and in the second region 50C protrude from betweenneighboring isolation regions 54. As illustrated, the top surfaces ofthe isolation regions 54 are above top surfaces of the lower epitaxialportions 60 and dielectric material 64 in the first region 50B and abovethe lower epitaxial portions 70 in the second region 50C. In otherembodiments, the top surfaces of the isolation regions 54 may be belowtop surfaces and above bottom surfaces of the lower epitaxial portions60 and dielectric material 64 and below top surfaces and above bottomsurfaces of the lower epitaxial portions 70, or the top surfaces of theisolation regions 54 may be below bottom surfaces of the lower epitaxialportions 60 and dielectric material 64 and bottom surfaces of the lowerepitaxial portions 70. Further, the top surfaces of the isolationregions 54 may have a flat surface as illustrated, a convex surface, aconcave surface (such as dishing), or a combination thereof. The topsurfaces of the isolation regions 54 may be formed flat, convex, and/orconcave by an appropriate etch. The isolation regions 54 may be recessedusing an acceptable etching process, such as one that is selective tothe material of the isolation regions 54. For example, a chemical oxideremoval using a CERTAS® etch or an Applied Materials SICONI tool ordilute hydrofluoric (dHF) acid may be used.

Processing may then proceed as discussed with respect to FIGS. 15through 23C and steps 234 to 256 to achieve the structure illustrated inFIGS. 23A, 23B, and 23C, or similar.

FIG. 57 illustrates a modification to the process and structuresdiscussed with respect to FIGS. 46 through 55, and 15 through 23C. FIG.57 illustrates a cross-sectional view of a structure after processingthrough the processes discussed with respect to FIGS. 46 through 52 andafter a conversion process. In FIG. 57, the lower epitaxial portions 60are converted to a dielectric material 64. The conversion process may besimilar to that discussed above with respect to FIG. 53, and may be, forexample, for a longer duration, at a higher temperature, the like, or acombination thereof. In the illustrated embodiment in FIG. 57, the lowerepitaxial portions 60 are converted to a dielectric material 64 to anextent such that a discontinuous region of the lower epitaxial portion60 remains between the upper epitaxial portions 62 and respective fins52. Discontinuities 130 are illustrated. Processing may then proceed asdiscussed with respect to FIGS. 54, 55, and 15 through 23C to achievethe structure illustrated in FIGS. 26A, 26B, and 26C, or similar.

FIGS. 58 through 60 illustrate various depths to which the isolationregions 54 may be recessed, for example in FIGS. 12, 35, and 55. FIGS.58 through 60 correspond to aspects of FIG. 15 and various modificationsdiscussed herein. As illustrated in FIG. 58, the top surface of theisolation region 54 is above a top surface of the lower epitaxialportion 60 and dielectric material 64. As illustrated in FIG. 59, thetop surface of the isolation region 54 is between a top surface of thelower epitaxial portion 60 and dielectric material 64 and a bottomsurface of the lower epitaxial portion 60 and dielectric material 64. Asillustrated in FIG. 60, the top surface of the isolation region 54 isbelow a bottom surface of the lower epitaxial portion 60 and dielectricmaterial 64. These modifications can be incorporated into any of theprocesses and structures discussed above.

FIGS. 61 through 63 are transmission electron microscopy (TEM) images ofsamples in accordance with embodiments. FIG. 61 illustrates a fin 52 andan epitaxial fin comprising a lower epitaxial portion 60 and an upperepitaxial portion 62. The lower epitaxial portion 60 has been oxidizedto form a dielectric material 64, and the lower epitaxial portion 60remains continuous. In the embodiment of FIG. 61, the fin 52 is silicon,the lower epitaxial portion 60 is Si_(1-x)Ge_(x), where x>=0.10, theupper epitaxial portion 62 is silicon, and the dielectric material isSiGeO.

Similarly, FIG. 62 illustrates a fin 52 and an epitaxial fin comprisinga lower epitaxial portion 60 and an upper epitaxial portion 62. Thelower epitaxial portion 60 has been oxidized to form a dielectricmaterial 64, and the lower epitaxial portion 60 is discontinuous withdiscontinuities 130. In the embodiment of FIG. 62, the fin 52 issilicon, the lower epitaxial portion 60 is Si_(1-x)Ge_(x), wherex>=0.10, the upper epitaxial portion 62 is silicon, and the dielectricmaterial is SiGeO.

FIG. 63 illustrates a fin 52 and an epitaxial fin comprising a lowerepitaxial portion 60, a template layer 142, and an upper epitaxialportion 144. The lower epitaxial portion 60 has been oxidized to form adielectric material 64, and the lower epitaxial portion 60 remainscontinuous. In the embodiment of FIG. 63, the fin 52 and template layer142 are silicon, and the lower epitaxial portion 60 and upper epitaxialportion 144 are Si_(1-x)Ge_(x), where x>=0.10. The dielectric materialis SiGeO.

Embodiments may achieve advantages. For example, by allowing for theupper epitaxial portions of the epitaxial fins to be strained, carriermobility through a channel region of a finFET may be increased. Further,embodiments may form a partial or full omega gate on a finFET. Forexample, where a continuous lower epitaxial portion remains in anepitaxial fin, an omega gate may be partial, whereas when adiscontinuous lower epitaxial portion remains in an epitaxial fin, anomega gate may be full. Some embodiments may therefore decrease aleakage current through the fin and substrate.

An embodiment is a structure. The structure comprises a fin on asubstrate, isolation regions on the substrate, a dielectric region, anda gate structure. The fin includes a first epitaxial portion. Theisolation regions are on opposing sides of the fin, and at least thefirst epitaxial portion of the fin protrudes from between the isolationregions. The dielectric region directly underlies the first epitaxialportion. A material of the dielectric region is different from amaterial of the isolation regions. The gate structure is along sidewallsand is over an upper surface of the fin. The gate structure defines achannel region in the first epitaxial portion.

Another embodiment is a structure. The structure comprises a channelregion, an intermediate region directly underlying the channel region, agate structure over the channel region, and source/drain regions onopposing sides of the channel region. The channel region comprises afirst crystalline semiconductor material. The intermediate regioncomprises a second crystalline semiconductor material and a dielectricmaterial. The dielectric material is a derivative of the secondcrystalline semiconductor material.

A further embodiment is a method. The method comprises epitaxiallygrowing a first crystalline semiconductor material on a substrate andepitaxially growing a second crystalline semiconductor material abovethe first crystalline semiconductor material. After epitaxially growingthe first crystalline semiconductor material and the second crystallinesemiconductor material, the first crystalline semiconductor material andthe second crystalline semiconductor material form a fin on thesubstrate. The method further comprises after epitaxially growing thesecond crystalline semiconductor material, converting at least a portionof the first crystalline semiconductor material in the fin to adielectric material, forming a gate structure over the fin, and formingsource/drain regions on opposing sides of the gate structure.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A structure comprising: a fin on a substrate, thefin comprising a first epitaxial portion; isolation regions in thesubstrate and on opposing sides of the fin, at least the first epitaxialportion of the fin protruding from between the isolation regions; adielectric region directly underlying the first epitaxial portion, amaterial of the dielectric region being different from a material of theisolation regions, upper surfaces of the isolation regions being abovean upper surface of the dielectric region; and a gate structure alongsidewalls and over an upper surface of the fin, the gate structuredefining a channel region in the first epitaxial portion.
 2. Thestructure of claim 1, wherein the fin further comprises a secondepitaxial portion directly underlying the first epitaxial portion, thematerial of the dielectric region comprising an insulating derivative ofa material of the second epitaxial portion.
 3. The structure of claim 2,wherein the second epitaxial portion continuously connects the firstepitaxial portion to a crystalline material of the substrate.
 4. Thestructure of claim 2, wherein the second epitaxial portion isdiscontinuous between the first epitaxial portion and a crystallinematerial of the substrate.
 5. The structure of claim 2, wherein amaterial of the first epitaxial portion is silicon, the material of thesecond epitaxial portion is silicon germanium, and the material of thedielectric region is silicon germanium oxide.
 6. The structure of claim1, wherein the fin further comprises a template epitaxial portiondisposed between the first epitaxial portion and the dielectric region.7. The structure of claim 1, wherein the fin further comprisessource/drain regions on opposing sides of the gate structure, thechannel region being disposed between the source/drain regions.
 8. Astructure comprising: a channel region over a fin and comprising a firstcrystalline semiconductor material, the fin protruding above asubstrate; an intermediate region over the fin and directly underlyingthe channel region, the intermediate region comprising a secondcrystalline semiconductor material and a dielectric material, thedielectric material surrounding sidewalls of the second crystallinesemiconductor material and being a derivative of the second crystallinesemiconductor material; a gate structure over the channel region; andsource/drain regions on opposing sides of the channel region.
 9. Thestructure of claim 8, wherein the first crystalline semiconductormaterial is different from the second crystalline semiconductormaterial.
 10. The structure of claim 8, wherein the second crystallinesemiconductor material is continuous from an upper surface of theintermediate region to a bottom surface of the intermediate region. 11.The structure of claim 8, wherein the second crystalline semiconductormaterial is discontinuous from an upper surface of the intermediateregion to a bottom surface of the intermediate region.
 12. The structureof claim 8 further comprising a template region disposed between thechannel region and the intermediate region.
 13. The structure of claim8, wherein the first crystalline semiconductor material is silicon, thesecond crystalline semiconductor material is silicon germanium, and thedielectric material is silicon germanium oxide.
 14. A semiconductorstructure comprising: a substrate with a first region and a secondregion; an N-type device in the first region, the N-type devicecomprising: a first semiconductor fin over the substrate and betweenisolation regions in the first region; a first upper epitaxial portionover the first semiconductor fin, the first upper epitaxial portioncomprising a first material and protruding above the isolation regionsin the first region; a first lower epitaxial portion between the firstupper epitaxial portion and the first semiconductor fin, the first lowerepitaxial portion comprising a second material different from the firstmaterial; and a dielectric material around the first lower epitaxialportion; and a P-type device in the second region, the P-type devicecomprising: a second semiconductor fin over the substrate and betweenisolation regions in the second region; a second upper epitaxial portionover the second semiconductor fin, the second upper epitaxial portioncomprising a third material different from the first material andprotruding above the isolation regions in the second region; a secondlower epitaxial portion between the second upper epitaxial portion andthe second semiconductor fin, the second lower epitaxial portioncomprising the second material; and the dielectric material around thesecond lower epitaxial portion.
 15. The semiconductor structure of claim14, wherein the P-type device further comprises a template layer betweenthe second upper epitaxial portion and the second lower epitaxialportion, wherein the template layer comprises the first material. 16.The semiconductor structure of claim 14, wherein the first lowerepitaxial portion has a width smaller than a width of the first upperepitaxial portion.
 17. The semiconductor structure of claim 16, whereinthe second lower epitaxial portion has a width smaller than a width ofthe second upper epitaxial portion.
 18. The semiconductor structure ofclaim 14, wherein the dielectric material is an oxide of the secondmaterial.
 19. The semiconductor structure of claim 14, wherein the firstmaterial is silicon, the second material is silicon germanium, and thedielectric material is silicon germanium oxide.